It is known in the art to provide a motion picture camera (especially a small camera for amateur use) with sound recording means comprising a magnetic recording head, a capstan for advancing the film at a uniform rate past the recording head, a pressure member which presses the film strip tightly against the magnetic head, a drum or puck which presses the film against the capstan to provide a frictional drive of the film by the capstan, and a loop sensor or feeler for sensing the film loop between the optical film gate and the recording head. In the usual known construction, the magnetic recording head and the capstan are mounted in fixed locations in the camera, whereas the pressure member, the drum, and the loop feeler are adapted to be removed from their operating positions, to leave space for inserting the film strip when the camera is being loaded with fresh film.
In prior cameras of this type, it has been customary to make the pressure member, the capstan, and the loop feeler each individually movably guided in a separate slit or guideway in a mounting plate fastened in the camera, and connected with each other and with a control member by a lever mechanism which, upon actuation of the control member, moves the pressure member, the drum, and the loop feeler simultaneously out of their operating positions. In the prior art, the lever mechanism is arranged on what may be called the rear of the mountng plate, in order not to interfere with the guidance of the film in the vicinity of the magnetic head, the pressure plate, the capstan and drum, and the loop feeler. Since it is necessary to have a flywheel of considerable mass and large dimensions to insure absolute constancy of speed of the capstan, the flywheel has also been arranged on the rear of the mounting plate, that is, the opposite side of the plate from that on which the recording head and capstan are placed. Because of the relatively large dimensions of the flywheel, it cannot be arranged in a plane with the lever mechanism, and therefore (according to the prior art) must be in a location spaced from the rear surface of the mounting plate, to allow room for the lever which controls the position of the pressure member and drum to move close to the rear surface of the mounting plate, between it and the flywheel. In other words, the flywheel must be spaced from the rear surface of the mounting plate by a space a trifle greater than the thickness of the lever which is to move in this space. This undesirably increases the thickness of the assembly, making it unsuitable for installation in a compact narrow motion picture camera, such as used for narrow film, e.g., 8 millimeter film. Also, there is a relatively high cost for precision machining of the parts, in the above described construction used in the prior art.